Add editorconfig for default settings

- enable easy sync of editor configs across
  team members and IDE's

.editorconfig

+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.{js,json,vue,scss,rb,haml,yml}]
+indent_size = 2
+
+[*.{js,json,vue,scss,rb,haml,yml,md}]
+indent_style = space
+charset = utf-8

.gitlab/CODEOWNERS

@@ -56,6 +56,7 @@ Dangerfile @gl-quality/eng-prod
 /lib/gitlab/danger/ @gl-quality/eng-prod
 /scripts/ @gl-quality/eng-prod
 /scripts/frontend/ @gl-quality/eng-prod @gitlab-org/maintainers/frontend
+.editorconfig @gl-quality/eng-prod
 
 # Telemetry owner files
 /ee/lib/gitlab/usage_data_counters/ @gitlab-org/growth/telemetry

doc/development/contributing/style_guides.md

 # Style guides
 
+## Editor/IDE styling standardization
+
+We use [EditorConfig](https://editorconfig.org/) to automatically apply certain styling
+standards before files are saved locally. Most editors/IDEs will honor the `.editorconfig`
+settings automatically by default. If your editor/IDE does not automatically support `.editorconfig`,
+we suggest investigating to see if a plugin exists. For instance here is the
+[plugin for vim](https://github.com/editorconfig/editorconfig-vim).
+
 ## Pre-commit static analysis
 
 You're strongly advised to install

lib/gitlab/danger/helper.rb

@@ -133,6 +133,7 @@ module Gitlab
         %r{\A(\.gitlab-ci\.yml\z|\.gitlab\/ci)} => :engineering_productivity,
         %r{\A\.overcommit\.yml\.example\z} => :engineering_productivity,
         %r{\Atooling/overcommit/} => :engineering_productivity,
+        %r{\A.editorconfig\z} => :engineering_productivity,
         %r{Dangerfile\z} => :engineering_productivity,
         %r{\A(ee/)?(danger/|lib/gitlab/danger/)} => :engineering_productivity,
         %r{\A(ee/)?scripts/} => :engineering_productivity,

spec/lib/gitlab/danger/helper_spec.rb

@@ -222,6 +222,7 @@ describe Gitlab::Danger::Helper do
       'lib/gitlab/danger/foo'                                 | :engineering_productivity
       'ee/lib/gitlab/danger/foo'                              | :engineering_productivity
       '.overcommit.yml.example'                               | :engineering_productivity
+      '.editorconfig'                                         | :engineering_productivity
       'tooling/overcommit/foo'                                | :engineering_productivity
 
       'lib/gitlab/ci/templates/Security/SAST.gitlab-ci.yml'   | :backend